This application is based on Japanese Patent Applications No. 2001-153412 filed on May 23, 2001, and No. 2001-223436 filed on Jul. 24, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a control apparatus of an internal combustion engine.
2. Related Art
A car manufactured in recent years is provided with a catalyst such as a three-way catalyst, which is used for purifying exhausted gas, on the exhaust pipe of the car. At a cold start in which the engine is started at a low temperature of the engine and the catalyst, the ignition timing is retarded to increase the temperature of the exhausted gas. The increased temperature of the exhausted gas in turn promotes the heating of the catalyst so that the temperature of the catalyst is increased to a value in an active temperature range at an early time.
If the ignition timing is retarded in order to heat the catalyst at an early time, however, the engine torque decreases. In order to prevent the engine torque (or the engine speed) from decreasing, an idle speed control system (ISC) is used to increase the opening of an ISC valve (or a throttle valve) in order to raise an intake air quantity. As a result, the negative pressure of the intake air increases, reducing a difference between the negative pressure of the intake air and the atmospheric pressure. Accordingly, a braking force amplification effect of a brake booster inevitably becomes smaller.
In order to solve the above problems, as is disclosed in U.S. Pat. No. 5,497,745, with the initial value of the ignition timing at a cold start set at a target retard angle, ignition retarding control (or catalyst-early-heating control) is started and an intake manifold negative pressure is compared with a threshold value at predetermined control intervals. The threshold value is an intake manifold negative pressure required for assuring a proper negative pressure in a brake booster. If the intake manifold negative pressure is smaller than the threshold value, the ignition timing is retarded. If the intake manifold negative pressure is greater than the threshold value, on the other hand, the ignition timing is advanced.
As described above, with the technology disclosed in the U.S. patent, the initial value of the ignition timing at a cold start is set at a target retard angle and then the ignition timing is retarded or advanced in dependence on the intake manifold negative pressure. At a cold start, however, the fuel stability of the engine is poor so that, if the ignition timing is much retarded from the cold start as is the case with the disclosed technology, the fuel condition becomes unstable, unavoidably increasing the quantity of an exhausted unburned gas component such as HC or CO. In addition, if the ignition timing is much retarded from the cold start, the retard angle for the ignition timing causes a delay of the decreasing of the intake manifold negative pressure. Thus, it inevitably takes a longer time for the intake manifold negative pressure to decrease from a pre-start pressure (that is, the atmospheric pressure) to the threshold value, which is an intake manifold negative pressure required for assuring a proper brake booster negative pressure as described above. In the mean time, the negative pressure of the brake booster cannot be assured at a sufficient value so that the performance of the brake booster cannot be fully displayed. In short, with the disclosed technology, it is difficult to assure a sufficient negative pressure of the brake booster while reducing the exhaust emission at a start of the engine at the same time.
On the other hand, U.S. Pat. No. 3,129,802 discloses a technology whereby the closing timing of an intake valve is retarded when the pressure in a negative pressure tank for a brake booster is determined to be on the positive pressure side relative to a predetermined pressure. There is already known an apparatus (VVT) for adjusting a valve timing as is disclosed in JP-A No. S59-119007. The VVT is controlled to realize a valve timing proper for the operating state of the engine. The VVT is provided for achieving one of important objectives to improve the state of combustion. By execution of advancing control on the VVT in accordance with reduction of the negative pressure, however, the state of combustion cannot be improved sufficiently.
In addition, if the ignition timing is retarded in order to heat the catalyst at an early time, the resulting negative pressure is not sufficient as described above. Thus, with the technology disclosed in U.S. Pat. No. 3,129,802, advancing control is executed on the VVT in accordance with a negative pressure signal, resulting in an unimproved state of combustion.
It is thus an object of the present invention addressing the problems to provide an internal combustion engine with a control apparatus capable of assuring a required negative pressure at a start time of the engine and at a time immediately following the start time.
It is another object of the present invention to provide an internal combustion engine with a control apparatus capable of assuring a negative pressure required by a brake unit during a period in which early heating control of a catalyst is executed.
It is a further object of the present invention to provide an internal combustion engine with a control apparatus capable of assuring a negative pressure required by a brake unit at a start time of the engine and at a time immediately following the start time.
It is a still further object of the present invention to provide an internal combustion engine with a control apparatus capable of realizing early heating control of a catalyst and assuring a negative pressure required by a brake unit.
It is a still further object of the present invention to provide an internal combustion engine with a control apparatus capable of reducing the amount of obstruction resulting from control to assure a negative pressure required by a brake unit to control to heat a catalyst at an early time and control of a valve timing to improve combustion.
In order to achieve the objects described above, in accordance with an aspect of the present invention, an internal combustion engine is provided with a control apparatus, wherein a negative pressure recognizing means recognizes a negative pressure of an intake pipe or a negative pressure of a brake booster, and an ignition retarding control means starts ignition retarding control after the negative pressure reaches a level equal to or lower than a predetermined value. When fuel stability is poor at a cold start, instead of retarding an ignition timing, the ignition timing is set at a timing that improves the state of combustion so that it is possible to lower a pressure in an intake pipe at an early time while suppressing generation of unburned gas components such as HC and CO. Thus, at a point of time a negative pressure in the intake pipe (or a negative pressure of a brake booster) becomes equal to or lower than a predetermined value allowing a proper negative pressure of the brake booster to be assured, the ignition retarding control is started to retard an ignition timing and, hence, increase the temperature of exhausted gas so that the catalyst can be heated at an early time.
In this configuration, the time between the start of the engine and the completion of the catalyst heating may become slightly longer. By delaying the start timing of the ignition retarding control, however, it is possible to suppress generation of unburned gas components such as HC and CO. Caused by deterioration of a combustion state at a start of the engine, the generation of unburned gas components is the main cause of deterioration of emission at the start of the engine. Thus, it is possible to reduce the total emission quantity during the time between the start of the engine and the completion of the catalyst heating. As a result, it is possible to assure a negative pressure of the brake booster at an early time while reducing the exhaust emission at the start of the engine at the same time.
In accordance with another aspect of the present invention, the ignition retarding control can also be started after a predetermined time has lapsed since a start of the engine. In this case, a time it takes for the negative pressure in the intake pipe (or the negative pressure of the brake booster) to decrease to a level equal to or lower than a predetermined value is measured in advance by simulation, an experiment or the like with the start of the engine used as a reference point. The measured time is used as the predetermined time. Thus, by commencing the ignition retarding control after the predetermined time has lapsed since a start of the engine, the objective can be achieved in a simple configuration not employing a negative pressure recognizing means.
In accordance with a further aspect of the present invention, a retardation speed of the ignition timing is reduced till the negative pressure recognized by a negative pressure recognizing means decreases to a level equal to or lower than a predetermined value and, after the negative pressure has decreased to a level equal to or lower than the predetermined value, the retardation speed of the ignition timing is raised. In this case, during a period of time beginning from a start of the engine, the retardation speed of the ignition time is low, resulting in a small retardation quantity. Thus, the retardation of the ignition timing has only a small effect on the negative pressure in the intake pipe and, in addition, the state of combustion does not deteriorate so that it is possible to lower the negative pressure in the intake pipe in a short period of time while reducing the quantity of a generated unburned gas component. Then, after the negative pressure in the intake pipe (or the negative pressure of the brake booster) has decreased to a level equal to or lower than the predetermined value, the retardation speed of the ignition timing is raised so that it is possible to increase the catalyst heating effect provided by the retardation of the ignition timing. It is thus possible to assure a negative pressure of the brake booster at an early time while reducing the exhaust emission at a start of the engine at the same time. In addition, since the ignition retarding control is commenced from a start of the engine, a period of time from the start of the engine to completion of catalyst heating can be shortened.
In accordance with a still further aspect of the present invention, a retardation speed of the ignition timing is reduced till a predetermined time lapses since a start of the engine and, after the predetermined time has lapsed, the retardation speed of the ignition timing is raised.
In accordance with a still further aspect of the present invention, the ignition timing""s retardation quantity and/or retardation speed are set on the basis of a negative pressure recognized by the negative pressure recognizing means in the course of the ignition retarding control. In this way, it is possible to increase the temperature of exhausted gas by retarding the ignition timing as much as possible in a range allowing a proper value of the negative pressure of the brake booster to be assured and, hence, shorten the time to heat the catalyst while assuring the negative pressure of the brake booster at an early time and preventing the state of combustion from worsening.
In accordance with a still further aspect of the present invention, the ignition timing""s retardation quantity and/or retardation speed are set on the basis of a sum of differences between negative pressures recognized by the negative pressure recognizing means and a predetermined value or a maximum value of the differences. With the ignition timing""s retardation quantity and/or retardation speed set in this way, the negative pressure of the brake booster can be lowered to a proper negative pressure level in a short period of time by reducing the retardation quantity of the ignition timing and/or lowering the retardation speed of the ignition timing when the actual negative pressure of the brake booster is determined to be insufficient as indicated by a small sum of differences between negative pressures recognized by the negative pressure recognizing means and the predetermined value or a small maximum value of the differences. On the other hand, a large sum of differences between negative pressures recognized by the negative pressure recognizing means and the predetermined value or a large maximum value of the differences indicates that the negative pressure in the intake pipe (or the negative pressure of the brake booster) is sufficiently low, leading to a determination that a proper negative pressure of the brake booster can still be assured even if the negative pressure in the intake pipe slightly rises so that the catalyst heating effect based on retardation of the ignition timing can be enhanced by increasing the retardation quantity of the ignition timing and/or raising the retardation speed of the ignition timing in a range that does not deteriorate the combustibility.
In accordance with a still further aspect of the present invention, the ignition timing""s retardation quantity and/or retardation speed are set on the basis of a time lapsing since a start of the engine in the course of ignition retarding control. In detail, operations desirable for an ignition timing between a start of the engine and a heated state of the catalyst, that is, the negative pressure in the intake pipe (or the negative pressure of the brake booster), the temperature of the catalyst and the like can be estimated in advance by simulation, by conducting an experiment or by other means. Thus, from results of the estimation, it is possible to create table data, a formula or the like to represent a relation between a time lapsing since a start of the engine and a retardation quantity and/or a retardation speed, which are desirable for the ignition timing, in advance. The table data is stored in a memory. Then, by setting the ignition timing""s retardation quantity and/or retardation speed at values obtained from the stored table data or the formula in accordance with a time lapsing since an engine start at an actual start of the engine, desirable ignition retarding control can be executed. As a result, it is possible to assure a negative pressure of the brake booster at an early time while reducing the exhaust emission at a start of the engine at the same time.
In accordance with a still further aspect of the present invention, a control range (guard values) of the retardation quantity of the ignition timing are changed in accordance with a negative pressure recognized by the negative pressure recognizing means and/or a load borne by the internal combustion engine in the course of the ignition retarding control. An example of the load is a load to operate an auxiliary apparatus such as an air conditioner. In this way, the retardation quantity of the ignition timing can be controlled to a desirable value in accordance with the negative pressure in the intake pipe (or the negative pressure of the brake booster) and/or a load borne by the internal combustion engine. As a result, it is possible to assure a negative pressure of the brake booster at an early time while reducing the exhaust emission at a start of the engine at the same time.
In accordance with a still further aspect of the present invention, the ignition timing is further retarded when the engine is an idle operation state and a negative pressure recognized by the negative pressure recognizing means is lower than a predetermined value after a predetermined time has lapsed since a start of the engine. That is, in an idle operation state after a predetermined time has lapsed since a start of the engine, if the negative pressure in the intake pipe (or the negative pressure of the brake booster) is sufficiently low so that a proper negative pressure of the brake booster can be assured even if the negative pressure in the intake pipe slightly increases, the ignition timing is further retarded to further increase the temperature of exhausted gas. Thus, the time required for heating the catalyst can be shortened while a proper negative pressure of the brake booster is being assured.
In accordance with a still further aspect of the present invention, the negative pressure recognizing means is a pressure sensor for detecting a negative pressure of the brake booster or a means for estimating a negative pressure of the brake booster on the basis of the internal combustion engine""s operating conditions such as the negative pressure in the intake pipe, the intake airflow, the engine speed, the gear position, status of a brake switch and a brake operation count. By directly detecting a negative pressure of the brake booster by means of a pressure sensor, the negative pressure of the brake booster can be determined with a high degree of accuracy so that the control precision can be improved. In addition, by estimating a negative pressure of the brake booster on the basis of the operating conditions of the internal combustion engine, a negative pressure of the brake booster can be estimated from outputs of sensors and switches, which are generally provided for engine control so that it is not necessary to provide a new pressure sensor. As a result, a demand for a reduced cost can be met.
In order to achieve the objects of the present invention, in accordance with a further aspect of the present invention, an internal combustion engine is provided with a control apparatus, which is provided with a variable intake valve timing mechanism for setting an intake valve""s position relative to the crank shaft of the internal combustion engine at a variable value and used for controlling the closing position of the intake valve on the basis of a result of processing carried out on the closing position of the intake valve in accordance with an operating condition of the internal combustion engine. The control apparatus has a first advancing control means, which is used for advancing the closing position of the intake valve on the basis of the operating state of a brake when the closing position of the intake valve is retarded behind a control position of a bottom dead center.
Normally, a negative pressure is expended only when the brake is used. Thus, by advancing the closing position of the intake valve, a flow back to the intake pipe can be suppressed to maintain a negative pressure in the intake valve only when the negative pressure is expended. As a result, a negative pressure can be introduced into the intake pipe only when the negative pressure is necessary. Therefore, without providing a pressure sensor in a brake tank, a negative pressure in the intake pipe can be sustained at a negative level only when the negative pressure is needed in the intake pipe. It is thus possible to properly implement control for retarding the closing position of the intake valve typically in order to suppress a pumping loss or improve combustion.
Normally, when an ignition timing control means retards the ignition timing in order to heat the catalyst at an early time, the torque generated by combustion inevitably decreases. At that time, an intake airflow control means compensates the torque for its decrease by increasing the intake airflow in order to maintain a target revolution speed. With the intake airflow increased, the pressure in the intake pipe approaches the atmospheric pressure. Thus, with the ignition timing retarded, the brake is applied and the negative pressure is therefore expended. When the brake is applied next with the negative pressure expended, the driver needs to apply a large depressing force, which causes a feeling of incompatibility in the driver.
In accordance with a still further aspect of the present invention, an internal combustion engine is provided with a valve timing control apparatus, which is provided with a target revolution speed setting means for setting a target revolution speed of the internal combustion engine, an intake airflow control means for increasing an intake airflow by setting a throttle valve at a position on an opening side to control a revolution speed from a decreased value of the revolution speed to the target revolution speed, a catalyst converter provided on an exhaust pipe, an ignition timing control means for controlling an ignition timing in accordance with an operating condition of the internal combustion engine, and a variable intake valve timing mechanism for setting an intake valve""s position relative to the crank shaft of the internal combustion engine at a variable value and used for controlling the closing position of the intake valve on the basis of a result of processing carried out on the closing position of the intake valve in accordance with an operating condition of the internal combustion engine. The ignition timing control means has a configuration including a means, which is used for retarding the ignition timing from an ignition timing set on the basis of a normal operating condition of the internal combustion engine so that the catalyst converter is heated at an early time in a cold start of the internal combustion engine; and a first advancing control means, which is used for advancing the closing position of the intake valve on the basis of the operating status of a brake when the closing position of the intake valve is retarded behind a control position of a bottom dead center.
Thus, when the control to retard an ignition timing is executed, the position of the intake valve is retarded on the basis of the operating status of the brake. As a result, a flow back to the intake valve can be suppressed. Therefore, the pressure of the intake pipe can be made a negative pressure when it is necessary to introduce a negative pressure into the brake tank so that the brake tank can be sustained at a proper negative pressure and it is also possible to properly implement control for retarding the closing position of the intake valve typically in order to suppress a pumping loss or improve combustion even if the catalyst is being heated at an early time.